A smooth-surfaced conductor typically has low surface impedance, which results in the propagation of electromagnetic (EM) waves at the surface of the conductor at higher frequencies. Upon reaching an edge, corner or other discontinuity, these surface waves radiate, or scatter, resulting in interference. The presence of such interference, therefore, is a cause for concern for high-frequency device designers using conductive materials, such as, for example, ground planes or reflectors for antennas, microstrip transmission lines, inductors, and the like.
In an effort to minimize the deleterious effects of surface waves on a conductor, various techniques have been developed whereby texture is implemented at the surface of the conductor. The texture may be provided by a lattice of conductive structures that extend away from the surface of the conductor. Conductors having this surface texture frequently are referred to as “high-impedance surfaces.” The conductive structures of conventional high-impedance surfaces typically consist of a single metal plate, parallel to the surface of the conductor, and a metal post to connect the plate to the surface of the conductor. The metal post introduces an inductance proportional to its length while the capacitive coupling between the perimeters of adjacent conductive plates introduces capacitance to the surface of the conductor. The inductance and capacitance introduced by the lattice of conductive structures functions as a stop band filter that suppresses the propagation of surface waves within a stop band determined from the resonant frequency as defined by the inductance and capacitance introduced by the lattice of conductive structures. Accordingly, the conductive structures can be designed so as to achieve a stop band at the operational frequency of the high-frequency device, thereby minimizing the unwanted affects of the surface waves at the operational frequency. However, to achieve the inductance and capacitance necessary for a number of desirable operating frequency ranges, excessively large high-impedance surfaces often must be used due to the limited inductance and capacitance supplied by conventional conductive structures.
Accordingly, an improved high-impedance surface would be advantageous.